The invention relates to a pulley of sheet metal made by spin-roll forming, but more particularly, the invention relates to a spun pulley with a thick hub and a method of making the pulley.
In some pulley designs, machined hubs are attached to webs and rims formed of sheet metal. A sheet metal web (or disc) and rim may be attached to a machined hub such as by bolts attached to a spider as disclosed in General Motors Technical Bulletin TC01-007 (Feb. 14, 1997) or it may be attached to the hub such as by welding or brazing. A machined hub may provide complicated shapes and thicknesses that permit the pulley to be attached to more than one component. For example, the aforementioned General Motors Technical Bulletin discloses a hub with a spider that attaches to a cup shaped sheet metal pulley by means of bolts and lock washers. The hub has a bore that attaches to a shaft of a water pump pulley. The hub is sufficiently thick to include external threads which define a fastener for attaching the pulley to a clutch for a fan. The hub for attaching the clutch is in an oppositely facing direction from the rim of the pulley with its belt engaging surface. While a machined hub may provide complicated shapes for attaching to shafts, pulleys and clutches, it introduces the attendant problems of weight, expense, and manufacture, and a troublesome process of precisely attaching and aligning the web and rim to complete the pulley.
Hubs or pulleys of sheet metal may be shaped by press forming using a series of dies to form a drawn cup or by spin forming using mandrel and rollers or a combination thereof. For example, a pulley with an integral hub that is press formed is disclosed in U.S. Pat. No. 5,441,456 where the hub has a stepped bore as shown in FIG. 5 and a bore with spline receiving grooves as shown in FIG. 8. Another example of a pulley with an integral hub is shown in U.S. Pat. No. 4,824,422. A limitation with the press forming and spin forming processes is that the hub is of a limited thickness where it is always less than that thickness of the sheet metal from which it was made. Consequently, such hubs are of limited strength and are not readily adaptable for attachment to other components at the hub's external diameter.
German Patent No. 4444526 discloses a method of shaping a hub by spin forming where a shaping roller is pressed against a side of a spinning annular disc of sheet metal that is supported at an opposite side with a head stock mandrel. The shaping roller is moved progressively radially inwardly against the side of the rotating disc which displaces a portion of metal while thinning part of the disc in forming a side wall web having a thickness that is less than the original sheet metal thickness. An annular wave is formed as metal is displaced and which progressively axially extends. The shaping roller is moved axially and is followed by a shaping roller which presses the so annularly displaced metal against a mandrel while simultaneously forming a hub integral to the disc and having a thickness that appears to be about equal to that of the disc. Similarly, U.S. patent application Ser. No. 08/68898 discloses a spin-rolled forming process where the thickness of the hub is about equal that of the disc. Neither of these processes disclose a hub having a sufficient thickness to provide a means for attaching it at an external diameter to other components such as a threaded nut of a fan clutch.